Contamination of the gate oxide of power metal oxide semiconductor field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs) may result in a shift of the threshold voltage (V_TH) in the MOSFETs and IGBTs. This may cause problems when connecting several MOSFET cells or IGBT cells in parallel, as those switching on first (having a lower V_TH) have to carry a large part of the load current until the remaining ones (having a larger V_TH) switch on as well. The same may also apply to the switch-off process. If, in addition, the threshold voltage shifts to the point that it is outside the operating range of the drive, the MOSFET or IGBT can no longer be switched on and/or off, and/or may switch too soon.